The invention discloses a printer, which can detect a media sheet, and a method of detecting a media sheet in a printer, wherein especially the type of the media sheet can be detected.
The invention relates especially to media sheets used for instance in printers which are based on the inkjet principle. An inkjet printer fires little droplets of ink onto the used media sheet, where the droplets are absorbed. After drying of the ink of one droplet a more or less little printed dot remains on the media sheet according to the absorbency of the media sheet. Every media sheet accepts a maximum amount of ink due to its characteristic maximum absorption of humidity. If an inkjet printer is operated such that it fires more droplets than the media sheet can absorb, i.e., the adjusted amount of ink at the printer is higher than the maximum amount of ink of the media sheet, the surplus ink is not absorbed any more from the media sheet. The surplus ink, which is too much for absorption, causes two main problems. The first problem is, that the surplus ink is smeared over the media sheet onto areas, where corresponding ink is not desired. The second problem is, that the surplus ink remains in contact with the nozzle of the print head of the inkjet printer and dries on the nozzle. This causes a blockage of the nozzle of the inkjet printer. Due to this blockage many cleaning runs or even an exchange of the inkjet print head become necessary.
Media sheets as used for instance in printers like inkjet printers are mainly known as normal paper sheets, as photo paper sheets or as transparencies. These media sheets have a different maximum absorption of humidity due to their consistence. Hence, dependent on the used media sheet the printer should only print with the maximum amount of ink corresponding to the used media sheet to avoid a surplus of ink and, therefore, to avoid the above mentioned problems caused by surplus ink.
To protect the printer by and to relieve the user on adjusting the correct amount of ink in a printer driver, printers according to the prior art make use of a C-shaped photo-interrupter or a reflective sensor. However, both the C-shaped photo-interrupter and the reflective sensor have some disadvantages, which will be now described together with their function.
The C-shaped photo-interrupter comprises a light emitter and a light receiver, which are arranged opposite to one another on the ends of a C-shaped holding element with a gap in between. The light receiver receives in an undisturbed mode direct light emitted by the light emitter. If a non-transparency media goes through the gap between the light emitter and the light receiver and blocks the direct light, the light receiver is in a disturbed mode and does not receive any direct light any more. This blockage will cause a receiver output current change, which indicates, that a non-transparency sheet is placed in the gap in between the C-shaped photo-interrupter. This detector has the disadvantages, that the media sheet has to be guided through the gap of the detector or the gap of the detector has to be placed very exactly at the media path through the printer, respectively, and that the detector only detects the difference between transparencies and non-transparencies.
The reflective sensor comprises a light emitter and a sensor for detecting light, which was emitted by the light emitter and reflected by a media sheet. The reflective sensor detects the level of the reflected light to determine the media sheet type, as different media have different reflective characteristics. However, this detector has the disadvantages, that it largely depends on the distance as well as the angle between the media sheet and the detector, and that it is very difficult to characterize the reflective level of a transparency, as a transparency has both reflective and transparent characteristics. A slight change in the distance between the detector and the media sheet or a slight change of the angle of the media sheet with respect to the detector will cause very big output level changes.
An object of the invention is to detect a media sheet used in a printer with regard to its type and existence, wherein the way of detection is universally applicable, i.e., it should not require any changes of the media sheet path through the printer and should detect and identify media sheets reliably.
The object is achieved by a printer, which can detect media sheets, and a method of detecting a media sheet according to the independent claims.
A printer, which can detect a media sheet type, comprises: a light emitting source and a reflector, the light emitting source being capable of emitting light in a light emission direction towards the reflector, the reflector being arranged in light emission direction and being capable of reflecting light emitted by the light emitting source in a light reflection direction; a detector being arranged such that it can detect reflected light; and a controller connected to the reflector, the controller being capable of modulating a characteristic of the reflected light.
A method of detecting a media sheet in a printer according to the invention comprises the following steps: emitting light by a light emitting source towards a reflector; reflecting light emitted by the light emitting source by the reflector and/or a media sheet, which has a given type and which can be arranged between the light emitting source and the reflector, in a light reflection direction; generating a signal corresponding to reflected light by a detector; modulating a characteristic of the reflected light by a controller connected to the reflector; and using the signal generated by the detector for detecting the media sheet.
One advantage of the invention over the prior art is that not only transparencies and non-transparencies but also normal paper and photo paper can be identified. Another advantage of the invention is that the media sheets must not be guided outside a normal printing path of a printer, which is provided according to the invention. A further advantage of the invention is that the printer can be self-calibrated to ensure reliable measurement. Such a self-calibration possibility requires no user intervention and saves manufacturing process time and, therefore, reduces manufacturing costs.
The above and other objects, features and advantages of the present invention will become apparent from the following description and the appended claims, taken in conjunction with the accompanying drawings in which like parts or elements are denoted by like reference numbers.